Experiments in Color Vision

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EXRMNTS COLO VON

The eye as receny been found to be a isrmen of wonderful

ad uspeced verat.

cn peeve fu coor In Images

hich, accoring o casca teoie, shod be onochroac

From chidhood onward we enoythe richness of color i e worlround us, fascinate by he ques

tons: "Ho do we see color? ow doou know you see he same color I do?y do coors sometimes ix to giveuie deren coors? Since 66wen saac Newton discovered theproperties of the visile specrum, wehave slowly een earning he answers;nd we are nding tha the beauty of eouter word is fu matched by te echnical eauy of the mechanisms wherebye eye sees coor.

No suden of coor vision can fail oe awed he sensiive discernmen

wi which the eye responds o he variety of stimui i recives. Recenty ycoeagues nd hve earned ha timechanism is fr more wonderfu hanhad en thought. The ee makes distntons of amzing sutety. t does noed narly so much inormation s actua ows to it rom th verydayword. I can uid colored worlds of iown ou of inormate materias haave aways en supposed to e inhery dra and cooress.

Perhaps the e way to egin he

story is to consider two ses of experiments. The rs is he great originalwork of Newton whch se he stage forrtua al research in coor vision snceha me. The second is an apparenlyrvial modicton at everses some ofs asc concusions.

As is so ofen the case with ruly evoutionary insghts, the simpicity ofNewon's discover causes one o woer why no oe efore him had made i.He passed a narrow eam of sunlighthroug a prism and found tha it fnnedu into he and of coors we now athe isible spectrum: red, orange, yelow, green, lue, indigo and viole.hen he reersed the press, gaherin

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e ea ogeher with a second prism,he color vanised and wie lig reppeared. Nex he ried recomining

only par of he specru, inserig aslotted board o cu o all u cerainselected band ee dir o pe88 When e coined wo such bandsof coor, leing e rays mix on a screen,a third color appeared, generally oemcing a color lying beween hends in he specru

Le us repea his las experimen,pacing the opening in e oard uinside he ends of he narrow yellowand in he specru. When hese woyeow eas srie te creen, hey

comine, as Newon observed, o produce yellow.Now for our odicaion. In fron

of he slits we place a pair of blacnd-wie potographic transparencies.ach show he same scene: a colecionof riously colored ojects There is, ofcourse, no coor in the potographsThere are simply ligher and darerareas, fored y blac silver grains ontransparen celluloid. A glance a hetwo shows ha hey are no asoluelyidentical. Some of the obecs in he

scee re reprsened y areas which areighter n the rs photograp an in hesecond. Others are darker in he rst andighter in e second Bu al tha eiherphotograph can do is to pass more or essof the igh faing o its dieren regions

The yellow eams pass through hesetransparencies and fa on he screen.Bu now ey are no yelow! Somehow,when tey are coined in an image,ey ar o longer restriced o producing heir specral color. On thescreen we see a group of oecs whosecoors, tough pae and unsauraed, aredisticly red, gray, yeow, orange,green, bue, bac, rown and wte [ee

ottom photoph o pe J In hisexperien we are force o e asonishing cocusion that e rays are no n

hemselves coormaing Raer teyare bearers of informaio ha e eyeuses o assign appropriate color o various obecs in an image .

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This conclusion i diaerically opposed o e main line of develpentof color heory, whic £w ro ewon's experimens. e i uccessors,noably Thoas Youg, Jae ClerMaxwell and Hermann on elol,

were fascnated b he prole o ipe colors and the sensaions ha coulde produced by copoundi em.Newon hisef developed ui oodrues for predicing e colors a wulde seen hen ariou pectral ray weremixed o form a spo of lig on a creen.Tese rules can be uarie i geomerical diagrams, one of e ole ofwhich is te color riagle ee imt top o pe On oder ersionsof i we ca rad o he rsu of co

COLORED OBJECTS in the top picture n

the pposite page were poographed with

he special ual camera which appears at

left. Hre the two groudass screens of

te camera are left uncovere to sow ha

one imge is photographed thrgh a gree

lter and he other throug a e lter.

The images are photographe o ordiary

black-an-whie lm; hen blackadwhite

psitive transparencies are made frm

te negatives. In he boom phoograp

the "r rnsparecy is projeced hrough

red lter and the "gree withou ater. When the two images ar super

imposed o the screen a rigt, they repro

ce te obects i a full rage o color.

© 1959 SCIENTIFIC AMERICAN, INC



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ii s my prts f lr with sa of oor B

O it ws isvere that ight is wav tion the lassi ivestigatisf olor aquire a epy satisfigia basis Th orer f ors in thespetru follws waveegth th g-est visib waveegth flig t the ree f th spetrm n the shrtest t

the violt n. pure lr wu e singl wavegth; mpun rswoul be mixtures f pure rs.

I tryig t mth lrs y mixispetra stmuli Mxwe Helmhltzfu that three ieret wvelengthswer nough t eet ll mthes tht ths wavelegths h t be hsefrm the re reen n blue bs fthe spetrum rigl re greean lue ame t b le the primryors. O the sis f this eviee thevprpse a threer thery f r

visin. We ee ot it the etailshere The ntrl ie is that the eyerespos t three ieret kis f vibratin n tht r sesti is thersult f stimulatig th thr rspsesi varing egrees f stregth. Thus ithas bom an rtile f faith i staar tho tht th lr see t point i l f view epes n whtwavlgths ar issuig frm tht pita upon thir reltive stregths r i-tensitie

Now s w hv sen in ur mi

ation f Newts experiment the lihtt ay pint on the sreen was mpsef ny tw elw" wvelengths yetthe imag was fuly ore n as weshl s atr the olors in imges wllb akably stabl v when thovral rative strengths r itesitiesof th tw wavlengths r varie.

u ms

Is somthing wrg with lssialthery? This lng line f gret investi-

gators at hve bee mistke Thnswer is that their wrk ha vry little

COLOR EEN when log and shor rec

ods are illuminaed by closely spaced nar

row bands of wavelenghs are reproduced

in hese Flexichrome" phooaphs The

illuinain aeenghs are indicaed by

a! on he specrum under each phoo

graph These images coud no be phoo

graphed direc he esponse of colo l

o he iied rage of wavelenghs used

ere is very dieren fro ha of he

y. CFC C has aricialy e

rodued he coors seen by e eye by

djusing he coor in a Flexichroe pin

j

ONG AND HORT RECORD are provided by ansparenies of hese back-andwhie

phoogphs ade hrough a red e (top) and a green ler boo n projecio helong ecord top) is illuinaed by he longer of wo wavelenhs or bands of aveenghs,

and he shor record is illuminaed by h shorer waeengh o band of wavelenghs

to o with olor s w ormll se tThe ealt with spts f light prtiarly with pairs f spts tri tath o to other Th onusisth rahd wre th taitl assumdto app to al f olor snstin Thisassumto runs vry p ad has p-at al ur teahg xpt fo that

of fw vstigtors lik Hrig C.ess an the otmporary worrsrotha ason a Lo M Hurvih(wh hav stu th t prouo a or spot b a surru)

Th stu f olor visn unr t-ural odits oplt mags (asoppos to spots surous) s thusa uxplore teritory W hav bnworkig this territryth aturalimag situation as w al itfor thepast v ers I th rst of ths artileI shal dsrib sm of th surpriss wehav nuntr

To for th mag n our moitoo Nwtons xprimnt n twosets of lmnts a par of irnt ph

togaphs o th sam se an a pairo it wavlgths for iluminatngth t possb to a th pturesdrt trg in th labotorartr vg th rknss of theirdnt s ut as v phtogra-h w hv g at ths poit sp w to pdu th two piturs

s to a olr sparations that s tphotogaph th s through two ltrsthat pass dret ands of wavlgthsI this wa th l s sstmatiall x-pos to ogr wavgths omigfro th s i on as, a to short wavgths in th othr. In our -vstgats w usual us a ltrfor th ogr wavlegths an a grter or th shrtr

Now whe w llumit the tras-pars with prtia any pi fwavlgths an superimps th im-ags w obtain a or mag f wesn th ogr of th two through thlongwav phtograph an th shortrthrugh the hrtwave phtgraph we




obtain most o al of th coos i thoigina sc a i thi o acs.If w vs th pocss th cos vs, rs showing u as ugns so on

o eeh v Sho

It appas thfo that colos in

iages ais ot fom th choi ofwavelngth but from the itrla fonge a shorte wavelgths over theentir scn. Lt us now tst this piina hothesis b so futhe xeriments.

The are severa mo convenientys to combine imags tha i th angment of ton's exerimnt. Onef th simlst is to plac th tansparnies in two oina poctos, usinglts to temin th iuminatingavgths Th color photogaphs on

the over an at the bottom of age 85how imges forme in this wa.Vhen e ok ith lts a ot

sing sigl avelengths ut athbans of wavlengths; th bans havmo o ss ith pning on thrctristis of e ter It tuns out

tha the with of the ban makes ittie. The on uiemt thatth ogwavelegth hotogaph o, asw ca it, the log eco, shoul beiumiate b the onge ba an theshot cor" b the shote ban. In on of th bas ma be as wias th ntire visib spctrum In othwos it may b whit ight Th pho

togah on th covr an th oe hotogaph on pag 85, show th result ofusing a lt fo the long reco ano te (that is, white light) for theshot co

On vatag of this arangemet isthat an obsev can test th truth ofou hypothsis in simpe an rmatia. ccoing to classia theory theombination of e an white can resutin nothing but ink With no photograin eith pocto an with a re terhl in front of one of them, the sreen

is inee pik. ow the transaeiesare oppe into pae a te viewhanges instant to one of ful, viviolo If the e lter is taken awa, theoo isapears a we see a backanwhite piture. Whe the te is putbak, the oors srig rth gain

iiental vantge in usig efor te og eco n white f tshort ies in the ft tht the olos ruc ook bout the sme to coor ls they o to the eye Thus the imgca be photographe irectly. imore restite bns of aveeththe l, hih es not have the nefoun versatiity of the eye anot re

spon as the eye oes reroutionmust be rere rtiiy [see -gps ge 86

The proectors aor simpe y otesting another variabe brightness yaing polarizing lters i front of troctor's enses e n var hount of ight ehing the sce freh soure. With o trnsreis ite rojetor, but with the re lter stiver one lens, the sreen isays urge o pinks fom re to hite, a thestrengths o the to bems are hnge

en the hotographs re in ae, thoos of the imag on th cree host over a very consierable rage oreativ intensities

et us pause fr moent to onsierth impications of this ast mostra-tin emeber that the hotogrph

O'S EXPERMENT in mxg specra coors is shownmaicay a op ; he aus modiin of e experimen

hch a pair of black-and-wie ansencies is insered n

he ems, s diagrammed a boom. When slis and b are boh in

he yew bnd f e specum Newons arrangeme prdces aspo f yll n seen T mag boom onains a gam

f cl e les and in is diagam and ers in is ar

ce refe espeively o he log ecrd and he shor record.




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O AD SHORT RECORDS ae pepaed by hoophing a

scee wih he dua camea diagammed o m open ecan

ge epese n co oed es he e i n fon of h ong cod

is ed nd he oe i n fon of he sho cod is geen A compo s

img is fomd by supeimosing og d sho ecods ee o scen by mans of d ojeco (otto

spectral band) Now e draw up a two

dmensional graph [op of 8loting the percenge of aalable logaelengths on one axis and he per-ceage of lable shor waelengthson the other Ery pont o he ageca be located somewhere on hs grahEach tme we pot a pint, we ote exto t the color it had on he age

Wha eerges s map o ponts, eachassocated wth a color hen s nshed, we can see that the map s ddednto two sectons by the 4degree lnrunng from loer lef to upper rghThis s he lne o gray points I we hadput the sae ransparency n each projector, all the ponts would fall on hegray line, snce he percentage o aal

able lgh would be he sae a eery

pon e mage or bo preorsThe her colors arrae heseles a sstea wa abou e 5ereele \Var colors are aboe ool olors are below s t seems ha he portat sal scale s ot the Newtonaspecr Fr all s bauty he specr s spl he accdetal oseee arragng siml rer ofwaelngh The sgicant scale forages rus from arm colors throgheutral colors to cool colors

Repeatn our experent th dere llunang waelengths or bands,we nd ha or eery par that producesull color he poston o he colrs ohe coordnate graph remans the same

Thus we hae the rule we wre lookig

r rle ha ells us n adance whatlor we shall nd at any pont n anae We a ake any par o rasparees and easure their percentage ranssso arious regos of hepture he, before projectg he,we ca preic he colors hese areaswll hae e wll be rght proidedha he llumiat waelengths areapable slag all the colors Inases where e are ot, e musthage he ordnae ap accordnglyThus he ull se rules conssts of rp o crae lr plos, one foeach secto f he l ap a he bot-o of page 89

oe ha ea rae sse s




hat te top o te screen s wte andthe botto s dark t bot proectorsturned on we now ae an nnte aret o redtowhte raos on thescreen, dupcatng a tose at coudpossb occur n a coored age oweer, te are arranged n a strct rdered progresson ere s no ando-ness nd on he screen ere s no coor

onl a graded pnk waso repeat, en, te coors n a nat

ra age are deterned b te reate baance o ong and short wae-engts oer te entre scene, assunghat te reaonshp changes n a soewhat rando wa ro pon to pontWthn broad s, the actua alues the waeengts ake no derence,nor does e oerall aaabe brghness o each

e ndependence o waeengh adcolor suggess tat te ee s an aa

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ngl versatle nsrument Not onl s iadapted to see coor n te word o lghtn whch t has actua eoed, but also can respond wt a ul range o sensato in uch ore ed words ra-atc proo o s s proded b -oher seres o experents

s

In hese we use a par o ewngboxes tat superpose ar argeages b eans o seransparentrrors see digrm t bottom of ge Eac box contans tungsen amps,wch produce whe ght, to Juminateone record and a sodium lamp o llumnae the oher e turn on one iew-er, insertng the ong and short rns-parences and pacng a red er oerthe tungsten lap e compose imges ul coored, contanng greens nd

blues, althogh the shortest waelenghcoming rom the mirror les n he ellopart o the spectrum Now we rn nte second iewer, nserng a gree l-ter oer the whte lgtsource Aginhe image conans a gamut o color n-cludng red he obserer cn see hmages n both ewers at onceehshowng the same range o color bt

represenng derent sual worlds Inthe rst the sodum lght (wh a we-length o 58 mlmcrons) seres s hesortest aalabe waelengh and helpsto smulate the green and blue In hesecond t s the longes waelength ndsmulates red I the obserer stndsbck ar enough rom the ewer, he cnalso see te naural" coors n he roomaround hm. Here then s a hrd woldn which ellow s reall ellow

nother wa to use the geen lter inhe sed sodm iewe s to ld it

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PROPERTIES OF COORDINTE SYSTEM ae usraed n

hese dagrams. et ae the grphs o epemena suatons

hh do o prode a gamu o oor the mage. Suh stu

tons appr to grph s srght nes. t rgh the aes ar shown

to be trthb. hen gry ne dvdng warm and oo oors

s dsped oors move bu mantan her reatve postons.

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up to the eye instead of placg t front of the tungsten laps. Ths ltasse both the sodu waelegth ahe green band [see bottom grh onge 92]. Whe he looks aroud theoo the obserer sees red objcts asblack and the rest of the colors aswashedout gree. But whe he looks a

the picture n the second iewg box hesees t uite full of color iludig red

The color worlds of te ewers areproduced by pctures. Could we akephysical odels of these worlds populatig the with real objects whichwould show the sae colors as theags the ewers uder the saecoditios of lluiatio? We could ifoly we had the proper pigets. Thepigets the world aroun us are thebst we hae bee able to d that lookoloe ou lghtg: a spectru of

isible waelegths fro to

GAING

licros. Each of these iments re-ects a broad band of waelengths nits peak s o sharp [see agr at toof ge 901

Thus our coloring terials do notdstguish clearly between waelengthsthat are farly close together If we couldd gets wth uch rrower re-

sponse cures we would suspect thatthese ght proide full color in morerestricted world of lght world forexaple lghted by the waelengthsthat pass through the gree lter. I thebsece of such clorng mterls weight ontent oursels wth reatngths world photographically if we couldshow that this is possible. A oent'sstudy of the diagras on page willshow the exctig fct tht a twocolorsepartion photogrph i world of ybadwidth is the sae s a twocolor

photograph a world of any other bad

IGHNSSONRO

widthincludng our ow proided thawe ostulte tht a corrctly roortioned change the absorpto badof the pigmets gos alog wth hnge in the ndwidth of the worldTherefore we cn use our regular lonnd short pctures taken through thred nd gre ltrs to trsport or

seles into new words with ther ned pproriately rrow pigets.

h su chsm

The sodiuiewer deonstratiosuggests an imortant consderatio thawe hae not preiously entond although t is plit in wat has alreadybeen sad If the eye percees color bcorng longer ad shorter wae-lengths t ust establsh a balance pointor fulcru soewhere n betwee s

that all waelengths o oe sid of t

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radio tackig statios-sesitive eoug to each out half a milon

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ollins Radio ompay, woking with te Natioal Aeonautics

and Space Adminstration's Jet Populsio Laboratoy suppied

the compete downange Puerto Rcan tacking staton and most

the equipment o the Godstone Lake tracking facility used tomaintain successu cotact wit te Natona Aeonautics andSpace Administratons st Lua Pobe. oins also paticipated

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kept tab on Ponee IV. The Godstone tracking statio tackedPioneer IV or 83 ous out to a distace o 407000 miles.

Fo more than a decade olins scietists ad engineers have beeexporig adio pobems assocated wit te uppe reaces o theatmospee and space beyond. The compay has maintained a

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olins Radio ompany apidly is expadig its researc in spacestudes, incudig space navigatio radiowave propagation payloadinstumetatio ad eectonc systems or space veces

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2 "Gi reduce 0 .6 "GThis Is Envirometal Prtectio!

Lo ok at the above i l u stration, sho wing two Be n d x r d a t a s e n s o r s o n a

lctomag n etc sake table. N otie h e eft ha n d u n t w h h i s o u nted so i d y o t s c l l at n g e a d o f t h e hake. T h e m a g e i s b u rre beau s e a vibratory

p a b o u t . 1 87

d o b l e a m l i t u d e a t 35 c . s , e q u i n g n acceeron force

of 12 " g ' s , s b e n g a p l ied irect y to it.

Now l o o k at the r ight h a d u n t m o u ned on Ro b i n s o n e n g i n e e re

m o u

n t i n g � ys t m

. s o m e d fere n e ! T h e e a r age of ths eq u p e n t s h ows

h e typia ly h i h i s o atio effi eny (over 95%) of the R o i n s o n MET-LFLEX®

m o u i e s g .O t h e r R o b i s o n e s g n s r o i d e s i ot e t o n h g h e r f re u e n e

ere the i n t ote eahes " g ' s T h e n a u r a l f r e q u e n i e s o f s u m o u n t s y t e m s a e h e w i t h i n i i t s w h i h a e n o t r i i a l t o t h e e u m e n t

U t i i z i g t i s m o u n t i n g s ys te r ad i y e d u e s t he e n v r o n e n t to a e v e lasi ly toerate by any reasonaby we desgned eeron equen Suh o u t i m i n a t e t h e n e e o r o s t y a n d t i e o n s u i n g r u g g e d i a t o O v e - a l l s p a e a n w e i g h t a r e h e l t o a n u .

Because o the prove erformane and re a y rord of arorne omp o t w p o t e t e b y R o b n s o m o u n t i n g s , a n r e a s i n g n u m b e o m a c te ctc stry are noroatig Robso mt a g a c p m e s i g

P c e a e l a b l i t e

R O B N S O N 7� P l , .

F o r me r l y R O B I N S O N AV I A T I O N C . W es t C o as t E n g i n e e r i n g O f f c e : S a n t a M n a , C a i f

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DATA LAB DIV ISI ONCEC's Advanced Electonic Daa

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BRO 00 TO 1 YLLOWBROWN TO DARK BROWN

WHIT 100 TO 1 TO BLUISH-WHIT

YLLOW 0 TO 1 YLLOW TO OFFWHIT

YLLOW-GRN 0 TO TO YOW ORANG

BLU 1 0 TO 1 O BU GRN

GR N T O TO GRAYGRN

R D O DARK RD TO DARK ORANGRD

OR A N G O YOW O RDORANG

LMI S F TAL TY o olos ude vaiatio i eate ihtess o sample pai

o o d shot stimui e summized i this pica chat Second olum shos the

mechaism tio ( hai the bihtess o eithe o oth o the stimui) o hih coo

t et is eoizabe ai o stimuli used as 4 miimios ad 7 miimios

o expet hat the ihn o mn oo wi be ined bv the intp oa d tim Whteve we e bvding a thid pite, the via poewi emin an mazing one fom teevotionay point of view hy h aytem tht an wok o we with twopkge of infomtion evoved o wokbette with thee? And who knowhethe it wi not wok bette ti witfo o ve o moe?

ht doe the eye itef do in theeveydy wod of the f petm?Doe it make ony two aveage? Odoe it pt to bette e the new biit

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we hve dioveedthe biity to itingih hpy between imge oey ped wveength? Pehap ieate mny et of vege intead ot two o thee

Evn i moe thn two infomationhanne ed we fee that the bigmp i obvio om one to two. Moo the pbiitv o o ee ome n he. And hteve m be addedb moe hnne, the bi onept wiemin Coo in the nat img dpend on the andom intepy of ongeand hote wveength ove te totvi ed

TUTE L

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Q �: EM M � s

V EWEDUMVENG BXE e diammed shemticl Eh o these istumets po

duces le omposite ime mens o the semitnspet mio. Tunsten liht is

hite, ad is esticted to oe nds o veeths b mens o ooed tes

99

Experiments in Color Vision

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